In injection molding machines, the mold is opened and closed at a parting line; mating parts separate at the parting line and move away from each other in a direction parallel to the clamping force, with the force usually being provided by a hydraulic cylinder. Core parts of the mold are also typically opened and closed laterally by slides that open and close simultaneously with the mating parts. As the mating parts move, they engage with inclined cams or pins and actuate the moving of the slides.
When the mold is completely open and the cam pins are withdrawn from inclined bores in the slides, it becomes necessary to hold the slides aligned in their open position while removing the molded article and awaiting the next molding cycle. The slides are held in position to allow for reentry of the cam pin when the mold is to be reclosed. Although the slides must be firmly and accurately held in the open position, the slides must also release readily when the cam pins reengage the inclined bores in the slides, thereby moving the core parts laterally together until the mold is again closed.
The prior art discloses various ways of holding the slides in position when the mold is open. One mold construction employs a pull rod that projects laterally from each slide. The slide is urged outwardly by a pre-loaded compression spring or hydraulic cylinder that is, along with the pull rod, housed on the exterior of the mating parts. The slide abuts a stop plate when the mold is completely open. A number of disadvantages have been noted for this approach. First, the assembly that protrudes from the mating parts must be removed to provide clearance to insert or remove the mold. Second, the necessary pre-loading is an additional assembly operation and may be a cause of injury to the operator. In addition, the pressure of the spring is applied during the entire movement of the cams, and may result in galling of the surfaces of the cam pins or the bores in the slides.
Another prior retaining system employs a dowel pin inserted into the slide. When the slide travels to the open position, the dowel pin enters into a jaw-like opening of a stationary slide retainer. The jaw-like opening is shaped like a socket and exerts the gripping forces required to keep the slide in the open position. A small spring is placed crosswise in the end of the body of the slide retainer opposite the jaw-type opening to apply spring pressure to the jaws. Although this retainer system is positive locking, the repeated engagement and disengagement of the spring loaded retainer and dowel pin may result in galling of the surfaces of these parts with consequent loss of positioning accuracy when the slide is locked in the open position. Dimensioning of the parts is particularly critical. The extending dowel pin is subjected to large loads and may be susceptible to shearing or bending after many molding cycles. The dowel pin and locking retainer also require a substantial amount of clearance space in the mold parts to accommodate these structures.